Synthesis of Allylic Alcohols

the dehydroborylation process of Soderquist [2] has made easy accessibility of traMS-vinyl-9-BBN, which is cleanly converted to trans allylic alcohols in good yields (Eq. 6.4). 

Evidently, this procedure provides a remarkably simple, stereospecific synthesis of allylic alcohols that was previously possible only with more reactive organometallic compounds. 

Tabl 6.5 Conversion of alkynes into allylic alcohols [1]  

3-Dimethyl-l-butyne Butyraldehyde 7,7-Dimethyl-trans-5-octen-4-ol 55 

4-Dimethyl-2-pentyne Acetaldehyde 3,5,5-Trimethyl-trans-3-hexen.2-ol 69 

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Koncienski295 reported a new synthesis of allylic alcohols starting from the allylic sulfones via formation of epoxysulfones. 

Synthesis of Allylic Alcohol Xa. A 3.84 g sample of olefin VII was treated with m-chloroperoxybenzoic acid (MCPBA) in dichloromethane for 1.5 hours at 0°C and 2.5 hours at 20°C. The NMR spectrum of the crude product indicated a mixture of approximately 75% epoxide VIII and 25% IX (structural assignments based upon assumed epoxidation preferentially from the less hindered side). Purification by column chromatography furnished 0.61 g of IX and 2.58 g of VIII. The separation was performed for characterization purposes the crude epoxidation mixture was suitable for subsequent transformations. 

With an efficient synthesis of allylic alcohol 46 in our hands, our attention turned to the selective reduction of the double bond. As stated above, we intended to use the hydroxy group in 46 to deliver hydride from the same face as the hydroxy group. Mainly there were two methods available (i) transition metal-mediated hydrogenation and (ii) metal hydride reduction. 

Scheme 2,1,4,32 Pd-catalyzed asymmetric synthesis of allylic alcohols in the presence of bisphosphane 34,...

The Evans rearrangement can be driven to completion by the addition of a thiophile, such as trimethylphosphite (Scheme 26.19) 440 46 M This strategy allows the chemistry of the allyl phenyl sulfoxide, or other sulfur precursor, to be exploited before the allyl alcohol is unmasked.4 3 471 474 The addition of phenylsulfenyl chloride to an alkene, followed by the elimination of hydrogen chloride and subsequent rearrangement, provides a useful synthesis of allyl alcohols.473 475 The [2,3]-Evans sigmatropic rearrangement is concerted and allows for stereochemical transfer.476 477 The reverse reaction, formation of the allyl sulfoxide, results from the treatment of an allyl alcohol using a base followed by arylsulfenyl chloride to produce the allyl sulfoxide.478 479... 

Allylic alcohols from sulfones.1 Polish chemists have extended the Julia synthesis of alkenes (11, 474) to a synthesis of allylic alcohols. In the presence of 1 equiv. of BF3 etherate, a-alkoxy aldehydes react with lithiafed sulfones to form adducts that are converted to allylic alcohols on reduction with sodium amalgam. This reaction was developed specifically for a synthesis of prostaglandins from Corey s lactone-aldehyde, but should have wider application. 

The vinylic substitution allows the synthesis of allylic alcohols 95 bearing a vinyltellurium moiety that constitute synthons of the corresponding organometallics 96 (see Section 9.13.8.2) (Scheme 55).154... 

Synthesis of Allylic Alcohols (Grignared-like Synthesis)... 

We can illustrate the synthesis of allylic alcohols from allylic sulfoxides with this synthesis of the natural product nuciferal. We mentioned this route on p. 1257 because it makes use of a heterocyclic allyl sulfide to introduce an alkyl substituent regioselectively. The allyl sulfide is oxidized to the sulfoxide, which is converted to the rearranged allylic alcohol with diethylamine as the thiophile. Nuciferal is obtained by oxidizing the allylic alcohol to an aldehyde with manganese dioxide. 

Fig. 46 One-pot two-step synthesis of allylic alcohols. The reductive step is catalyzed by (R)-ADH from Lactobacillus kefir or by (S)-ADH from Rhodococcus sp., respectively. The coenzyme is regenerated by an excess of isopropanol...

When selenenic acids are generated in the presence of alkenes, addition reactions similar to those of selenenyl halides occur. Oxidation and syn elimination of the adducts (42) provide a convenient synthesis of allylic alcohols (equation... 

In a facile synthesis of allylic alcohols the w-terminal residue of an iso-prenoid compound (218) is epoxidized with NBS or peracetic acid, and the... 

In the course of our earlier studies on terpenylboranes we developed a simple transformation of a- into 3-pinene," and a stereoselective synthesis of allylic alcohols by the reduction of vinylic epoxides.12 An extension of these studies to contrathermo-dynamic isomerization of a-thujene, 2- and 3-carene,13 and kinetic resolution of vinylic epoxides by the reduction with terpenylboranes,14 is described. 

Scheme 44 General synthesis of allylic alcohols based on a-a]k)4ation of allylic sulfoxides followed hy [2,3]-sigmatropic rearrangement...

DIBAL-H is the reducing agent of choice for regioselective reduction of oc,(3-unsat-urated esters to allylic alcohols. Horner-Wadsworth-Emmons olefmation (see Section 8.3b) followed by DIBAL-H reduction provides a tandem synthesis of ( )-allylic alcohols. ... 

The role of allylic sulfoxides as homoaldol equivalents in the synthesis of ( )-allylic alcohols was summarized earlier. A more recent finding is that allylic sulfoxides are precursors for conjugated dienes (equation 70). The elimination is regioselective but stereorandom. The 2,3-rearrangement of propar-gylic sulfenates gives allenyl sulfoxides. Allenyl sulfoxides are valuable synthetic intermediates. They can be converted into stereochemically homogeneous allenes, e.g. (205 equation 71). ... 

A three-stage synthesis of allylic alcohols has been devised (Scheme 32)," which consists of (i) alkylation of a sulfone-stabilized allylic carbanion (ii) peroxy acid oxidation of the allylic sulfone to give a 2,3-epoxy sulfone and (iii) reductive elimination of the 2,3-epoxy sulfone to give the allylic alcohol. The overall strategy is similar to that of the Evans-Mislow allylic alcohol synthesis based on the 2,3-sig-matropic rearrangement of allylic sulfoxides. However, there are regiochemical advantages to the sul-... 

The selenoxide elimination of -hydroxy selenoxides, which takes place regioselectively away from the hydroxy group, e.g. as in equation (41), has been developed into a useful synthesis of allylic alcohols. Similar regioselective elimination is also observed for p-acyloxy selenoxides, as shown in equations (39) and (42), and for P-acylamino selenoxides e.g. 115 equation 46). However, the regioselectivity of elimination is less useful for P-chloro and P-amino selenoxides. -" ... 

Evans, D. A., Andrews, G. C., Fujimoto, T. T., Wells, D. Application of allylic sulfoxide anions as vinyl anion equivalents. General synthesis of allylic alcohols. Tetrahedron Lett. 1973, 1385-1388. 

Jones-Hertzog, D. K., Jorgensen, W. L. Regioselective Synthesis of Allylic Alcohols Using the Mislow-Evans Rearrangement A Theoretical Rationalization. J. Org. Chem. 1995, 60, 6682-6683. 

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